The objective of the Experimental Pathology Service Core is to provide Center members both routine and advanced capabilities in the visualization and quantitation of structural and in situ molecular alterations to tissues and cells following exposures to toxicants. The Core provides a number of services. These include: standard microscopic services; expertise in experimental design and implementation of morphological techniques; quantitative structural analysis and interpretation of morphological alterations; instrumentation and expertise for specialized imaging technique; and training, consultation and technical assistance for users. Over the last budget period, 40 Center members from all Research Cores used the services of this Core. The development of the Experimental Pathology Service Core is the result of the bringing together of service facilities for microscopy and imaging that already exist at the University of Arizona. The Core supports these facilities through its budget, oversight and faculty. To insure that the needs of Center members are met, an advisory committee was formed in 1997. The development of these facilities has been accomplished from various institutional mechanisms which provides the space (>4500 sq. ft.), supports technical staff (5.5 FTES), maintains service contracts and contributes to the purchase of instrumentation. The facilities available to the Core include: a Histology Service Core Laboratory (653 sq. ft.) located in the Department of Cell Biology and Anatomy; various Imaging Facilities which include equipment and personnel to perform electron microscopy, confocal microscopy and digital image analysis; a developing cell and molecular imaging resource in the Arizona Cancer Center. The primary use of the Core has been histological analysis. However, in response to the needs of Center investigators the Core will be expanding in two directions: application of molecular biological techniques to microscopic imaging; and digital image analysis and manipulation. The first direction will be accomplished by the increased effort (from 10 to 25%) of Dr. Claire Payne and the second through acquisition of new image analysis equipment which will allow investigators to directly image tissue sections and cells.